Bought this game a while ago and it worked 100% of the time. As of a few weeks ago it just doesn't work- I'll start up the game and the screen will go black and change resolution like it normally did when it was loading but then it just closes and then I'm back at my desktop. I've repaired the installation and uninstalled/reinstalled multiple times but besides that I have no idea what to do.

My problem was reversed - it crashed/didn't start at Start-Up when I bought it.

I have updated the driver of my card and then it worked.
So I suggest you check your drivers.